Typically, two-wire dimmer switches are coupled in series electrical connection between an alternating-current (AC) power source and a lighting load for controlling the amount of power delivered from the AC power source to the lighting load. A two-wire wall-mounted dimmer switch is adapted to be mounted in a standard electrical wallbox and comprises two load terminals: a hot terminal adapted to be coupled to the hot side of the AC power source and a dimmed hot terminal adapted to be coupled to the lighting load. In other words, the two-wire dimmer switch does not require a connection to the neutral side of the AC power source (i.e., the load control device is a “two-wire” device). Additionally, typical “three-way” dimmer switches may be used in three-way lighting systems and comprise at least three load terminals, but do not require a connection to the neutral side of the AC power source.
Such dimmer switches typically comprise a bidirectional semiconductor switch, e.g., a thyristor such as a triac or two field-effect transistors (FETs) in anti-series connection. The bidirectional semiconductor switch is coupled in series between the AC power source and the load and is controlled to be conductive and non-conductive for portions of a half cycle of the AC power source to thus control the amount of power delivered to the lighting load. Generally, dimmer switches use either a forward phase-control dimming technique or a reverse phase-control dimming technique in order to control when the bidirectional semiconductor switch is rendered conductive and non-conductive to control the power delivered to the load, and, thus, the lighting intensity of the load. The dimmer switch may comprise an on/off switch or a toggle actuator for turning the lighting load on and off and an intensity adjustment actuator for adjusting the intensity of the lighting load between a minimum intensity and a maximum intensity (i.e., a low-end intensity and a high-end intensity). Examples of prior art dimmer switches are described in greater detail in commonly-assigned U.S. Pat. No. 5,248,919, issued Sep. 29, 1993, entitled LIGHTING CONTROL DEVICE; U.S. Pat. No. 6,969,959, issued Nov. 29, 2005, entitled ELECTRONIC CONTROL SYSTEMS AND METHODS; and U.S. Pat. No. 7,687,940, issued Mar. 30, 2010, entitled DIMMER SWITCH FOR USE WITH LIGHTING CIRCUITS HAVING THREE-WAY SWITCHES, the entire disclosures of which are hereby incorporated by reference.
To save energy, high-efficiency lighting loads such as, for example, compact fluorescent lamps (CFLs) and light-emitting diode (LED) light sources are being used in place of or as replacements for conventional incandescent lamps. High-efficiency light sources typically consume less power and provide longer operational lives as compared to incandescent lamps. In order to illuminate properly, a load regulation device (e.g., such as an electronic dimming ballast or an LED driver) is coupled between the AC power source and the respective high-efficiency light source (i.e., the compact fluorescent lamp or the LED light source) for regulating the power supplied to the high-efficiency light source.
Additionally, a dimmer switch controlling a high-efficiency light source may be coupled in series between the AC power source and the load regulation device for the high-efficiency light source. Some high-efficiency lighting loads are also integrally housed with the load regulation devices in a single enclosure. Such an enclosure may have a screw-in base that allows for mechanical attachment to standard Edison sockets and provide electrical connections to the neutral side of the AC power source and either the hot side of the AC power source or the dimmed-hot terminal of the dimmer switch (e.g., for receipt of the phase-control voltage). The load regulation device is operable to control the intensity of the high-efficiency light source to the desired intensity in response to the conduction time of the bidirectional semiconductor switch of the dimmer switch.
Because high-efficiency lighting loads include load regulation devices, the dimming performance of such high-efficiency light sources typically differs from the dimming performance of conventional incandescent light bulbs. For example, conventional incandescent light bulbs can typically be controlled by a dimmer switch over a wide dimming range—i.e., a high maximum intensity and a low minimum intensity—whereas high-efficiency light sources may require a more narrow dimming range in order to stably maintain the light output. In particular, some high-efficiency light sources require a higher minimum intensity as compared to a conventional incandescent light bulb. In addition, there are many different manufacturers and types of high-efficiency light sources (and accordingly, load regulation devices), and the dimming performance of these light sources varies greatly among one another. These differences in dimming performance of these high-efficiency light sources can cause confusion—and even, frustration—for an end user when using, for example, a dimmer switch. Therefore, there exists a need for an improved two-wire load control device that can properly control the intensity of the high-efficiency light source and is easier for an end user to operate.